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                                                                   EXHIBIT 31(a)

                           DUSA PHARMACEUTICALS, INC.

                                  CERTIFICATION

I, D. Geoffrey Shulman, certify that:

1.   I have reviewed this quarterly report on Form 10-Q of DUSA Pharmaceuticals,
     Inc.;

2.   Based on my knowledge, this quarterly report does not contain any untrue
     statement of a material fact or omit to state a material fact necessary to
     make the statements made, in light of the circumstances under which such
     statements were made, not misleading with respect to the period covered by
     this quarterly report;

3.   Based on my knowledge, the financial statements, and other financial
     information included in this quarterly report, fairly present in all
     material respects the financial condition, results of operations and cash
     flows of the registrant as of, and for, the periods presented in this
     quarterly report;

4.   The registrant's other certifying officer and I are responsible for
     establishing and maintaining disclosure controls and procedures (as defined
     in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and we
     have:

     a)    Designed such disclosure controls and procedures, or caused such
           disclosure controls and procedures to be designed under our
           supervision, to ensure that material information relating to the
           registrant, including its consolidated subsidiaries, is made known to
           us by others within those entities, particularly during the period in
           which this quarterly report is being prepared;

     b)    Evaluated the effectiveness of the registrant's disclosure controls
           and procedures and presented in this report our conclusions about the
           effectiveness of the disclosure controls and procedures, as of the
           end of the period covered by this quarterly report based on such
           evaluation; and

     c)    Disclosed in this report any change in the registrant's internal
           control over financial reporting that occurred during the
           registrant's most recent fiscal quarter (the registrant's fourth
           fiscal quarter in the case of an annual report) that materially
           affected, or is reasonably likely to materially affect, the
           registrant's internal control over financial reporting; and

5.   The registrant's other certifying officer and I have disclosed, based on
     our most recent evaluation of internal control over financial reporting, to
     the registrant's auditors and the audit committee of the registrant's board
     of directors (or persons performing the equivalent functions):

     a)    All significant deficiencies and material weaknesses in the design or
           operation of internal control over financial reporting which are
           reasonably likely to adversely affect the registrant's ability to
           record, process, summarize and report financial information; and

     b)    Any fraud, whether or not material, that involves management or other
           employees who have a significant role in the registrant's internal
           control over financial reporting.

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Date:  August 10, 2004                   /s/ D. Geoffrey Shulman
                                         ---------------------------------------
                                         D. Geoffrey Shulman
                                         President and Chief Executive Officer
                                         (principal executive officer)